Video: Midsagittal skull

Hello, everyone. This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, we’re going to be talking about the midsagittal section of the skull.

So basically, what we’re going to be doing is cut the skull in half, as you can see here on this image, and then explore the different structures that can be seen here. That way, we can have a better understanding of how the different bones of the skull look like and how they interact with one another and so on and so forth.

Now, what I'm going to be doing on this tutorial specifically is describing the different bones, different sutures, also some foramina that we’re going to be seeing here, some sulci, sinuses, and other structures.

And we’re going to start off with the different bones and bony structures that are seen from the midsagittal section. And starting off with this one highlighted in green, this is known as the greater wing of the sphenoid.

Now, you’re looking at one right now because on the other side, the other half of the midsagittal section of the skull, you would find, of course, another one.

Now, the greater wings of the sphenoid bone arise posterolaterally from the body of the sphenoid.

Now, even though we cannot clearly see here from the midsagittal section of the skull, it’s worth remembering that every time we talk about the greater wing of the sphenoid, there are few foramina worth remembering—a few holes where specific structures will be passing through that are worth remembering.

One of them is known as the foramen rotundum through which the maxillary nerve passes through.

The other one is known as the foramen ovale through which the mandibular nerve and the accessory meningeal artery pass through.

And the other one is known as the foramen spinosum. And here, you will find that the meninge… or the middle meningeal vessels will pass through.

The next structure that you see here, highlighted in green, is also a wing known as the lesser wing of the sphenoid. And the lesser wings—because right now you’re looking at one, the other one is also seen on the other half of the skull—now, the lesser wings arise superolaterally from the body of the sphenoid. And here, you can also see a canal or a little hole where some important structures will pass through. And this is known as the optic canal through which, then, the optic nerve and also the ophthalmic artery will pass through.

Now, the next structure that you see, highlighted in green, is known as the nasal surface of the maxilla. And here, we see the nasal surface of this bone which is part of the maxilla or the part of the maxilla that contributes to the anterior wall of the nasal cavity as you can clearly see here.

Now, the part of the maxilla that we see in this section is part of the body of the maxilla because the entire maxilla is comprised of different structures, including the body, the frontal process, the zygomatic process, palatine process that you can see here as well, the alveolar processes, and other structures that are part of the maxilla that we’re going to discuss separately on a more detailed tutorial.

But now, we’re ready to move on to the next bone that you see, highlighted in green. This is known as the ethmoid bone, clearly seen here from the midsagittal section.

The ethmoid bone is a porous bone that consists of a perpendicular plate and two ethmoidal labyrinths that are attached to the cribriform plate, which is this structure right about here.

Now, it makes up the middle part of the visceral cranium and contributes to the formation of the orbit, also the nasal cavity, the nasal septum, and the floor of the anterior cranial fossa.

Now, the ethmoidal labyrinths contain the ethmoid sinuses.

Now, you’re seeing, highlighted in green, one of the structures that we talked about before on the previous slide which is known as the cribriform plate, and is part of the ethmoid bone, and lies within the ethmoidal notch of the frontal bone.

The cribriform plates form the roof of the nasal cavity, and it has many openings through which the olfactory fibers from the nasal cavity pass to, then, the cranial fossa. Hence the word cribriform which, then, in Latin means “perforated.” So you will be finding a lot of holes here on the cribriform plate which will, then, serve as passages for the different olfactory fibers.

We’re ready now to move on to the next structure that you see, highlighted in green. This is known as the perpendicular plate of the ethmoid bone. And the perpendicular plate of this bone is a thin lamina which runs vertically from the cribriform plate. It forms the part of the nasal septum by attaching to the septal cartilage inferiorly.

The next structure that you see here, highlighted in green, is known as the medial plate of the pterygoid process, which is an extension of the basal surface of the body of the sphenoid bone.

You can find a projection from the medial pterygoid process known as the pterygoid hamulus, which is found right about here, and as the name indicates, has a shape of a hook.

The next structure that you now see, also highlighted in green, found now laterally, and then we call it the lateral plate of the pterygoid process. And the lateral plate of the pterygoid process of the sphenoid is where the lateral... on the lateral surface, you’ll see the lateral pterygoid muscle attaching to it.

While, also, on the medial surface of this plate, you will find, then, another muscle attaching, which is the medial pterygoid.

Now, the lateral pterygoid plate forms, then, the medial wall of the infratemporal fossa and part of the pterygoid fossa from its lateral and medial walls, respectively.

As we move on, we’re going to talk about this bone that we already mentioned briefly on a different slide. This is known as the maxilla—the entire section here, the midsagittal section of the maxilla, which you see here on this image, highlighted in green.

And visible from this section, we can see the maxilla is involved in the formation of the nose, orbit, and also the palate.

The maxilla consists of different parts. One is the body. The other one is the zygomatic process, the frontal process, the palatine process, and the alveolar processes. In this section, we see the body of the maxilla right about here which contributes to many structures, including the anterior margin and floor of the orbit (right about here) and also the anterior wall of the nasal cavity (as you can see here) and also the inferior part of the infratemporal fossa.

We also see here the alveolar processes which form the upper dental arch which houses the upper teeth.

And from this list here, we’re going to focus a little bit on this structure that you see here, highlighted in green, which is known as the palatine process of the maxilla.

Now, the palatine process of this bone makes up the roof of the mouth and the floor of the nasal cavity, as you can clearly see here on this image.

And on this process, we find this structure here, that you can see here, a foramen known as the incisive foramen, which is located posterior to the upper incisors and is an opening through which the nasopalatine nerve (a branch of the maxillary nerve) and the greater palatine vessels pass through.

Now, we’re going to highlight here a bone that you can see also from the midsagittal section of the skull, which is known as the lacrimal bone. And the lacrimal bone is located at the medial wall of the orbit.

It is a small rectangular bone and it articulates with different structures that are worth highlighting here on this tutorial. One is the ethmoid bone, which articulates with the lacrimal bone. Other one is the maxilla, the frontal bone, and also the inferior nasal concha.

On the lateral surface which we cannot see here from this image, but on the lateral surface of this bone, we find the lacrimal groove which forms a fossa for the lacrimal sac and the nasolacrimal duct.

Now, the medial surface, which we see here on this image, will come in contact with the ethmoidal cells and contributes to the middle nasal meatus.

Still on different bones, we’re going to highlight another one that you see here in green. This is known as the nasal bone. And the nasal bone is a bilaterally symmetrical paired bone.

These bones build the bridge of the nose at the superior border and main body, while the inferior borders connect with the nasal cartilage forming the superior margin of the nasal aperture.

The next structure is also a bone that you see, now highlighted in green, the palatine bone.

Now, the palatine bone consists of a horizontal plate, which you can see here, which forms the posterior portion of the hard palate and also a perpendicular plate and a pyramidal process.

The next structure that you see here, highlighted in green, is a bone, and we have been talking about it on previous slides. If you remember correctly, some of these structures are part of the sphenoid bone.

Now, the sphenoid bone, as I mentioned, is comprised of four main parts: a body, a greater wing, a lesser wing, and a pterygoid processes, which we talked about them on this tutorial already. So we have here, as a reminder, the lesser wing, the greater wing. We have the body of the sphenoid, and then you do have here the different pterygoid processes, and the medial one, and the lateral one.

Now, this bone is sometimes referred to as the “wasp bone” or the “butterfly bone” because if you look at it superiorly, because of the wings, it does look like it has a shape of a wasp or a butterfly—quite a beautiful but intricate bone.

Now, the sphenoid makes up the middle part of the base of the skull and contributes to the floor of the middle cranial fossa.

The next one that you see, highlighted in green—and if you remember well from previous slides—we’re looking now at the alveolar process of the maxilla, which is a porous inferior extension of this bone which forms, then, the dental containing cavities in each quadrant where the upper teeth are, then, housed.

And we’re going to move on to the next one, a bone that you see, highlighted in green. This is known as the vomer. And keep in mind that we just added here the medial wall of the nasal cavity on this midsagittal section of the skull, so you can show… we can show you the vomer.

Now, the vomer is located between the left and right side of the nasal cavity and forms the posterior inferior aspect of the nasal septum.

This bone is bordered by other bones, as you can clearly see here on this image. And if I show you here, it is bordered inferiorly and also anteriorly by this bone. If you remember correctly, this is the maxilla.

And it is also bordered posteriorly by this bone, which is the sphenoid.

The ethmoid bone is, then, located on the anterior superior aspect of the vomer. And you can see here the palatine bone, which borders it on its posterior inferior aspect.

We’re now ready to move on to another structure that we now see on the lateral wall of the nasal cavity. And this structure is known as the superior nasal concha, which is one of the three nasal conchae and is the smallest of all three, as you can clearly see here on this image.

Normally, it is covered by pseudostratified columnar ciliated respiratory epithelium, and the superior nasal concha extends from the wall of the ethmoid labyrinth and forms the superior nasal meatus inferiorly. Important to highlight about the superior nasal concha, that it drains the sphenoethmoidal recess and the sphenoidal sinus.

Now, we are moving on to the next structure, this is known as the middle nasal concha, which is located below the superior nasal concha and this structure here, which is known as the superior nasal meatus.

Now, the projection of the middle nasal concha forms the middle nasal meatus. It is also covered by pseudostratified columnar ciliated respiratory epithelium. Also, important to add that it drains the middle nasal meatus, the middle ethmoidal sinus, the frontal sinuses, and the maxillary sinus.

The last of these three conchae, we find this one here below all the other two, known as the inferior nasal concha, which is, then, located below the middle nasal concha, as you can clearly see here.

And unlike the middle and superior nasal conchae, the inferior nasal concha is a bony structure on its own and is not formed from the ethmoid labyrinth.

It is covered by pseudostratified columnar ciliated respiratory epithelium, and also important to add here that it drains the inferior nasal meatus and the nasolacrimal duct.

Now, we’re looking at this structure here, which is known as the crista galli meaning “crest of the rooster” in Latin. This is a small vertical projection on the top of the cribriform plate. And this projection will serve, then, as attachment for the falx cerebri.

Ready to move on to the next structure, this time a bone, seen on the midsagittal section of the frontal bone, highlighted here in green.

And as you remember, the frontal bone is comprised of different structures including a squamous part, orbital part, and a nasal part. And you can see them here on this section. So you have here the squamous part, the orbital part, and here, the nasal part.

Now, the squamous part makes up the largest part of the frontal bone and houses the frontal sinuses, as seen in this section. The orbital part of the frontal bone makes up the roof of the orbit, the ethmoidal sinuses, and the ethmoidal air cells which are located in the ethmoidal notch.

Now, the next structure that you see here, highlighted in green, is known as the parietal bone.

The parietal bones are paired bones found on either side of the neurocranium. The internal surfaces of the parietal bones are covered by these grooves that you see here, which are formed by the arterial pressure from the middle meningeal artery.

Next bone that we also see here, this is known as the temporal bone. And the temporal bone forms the base of the cranial fault and makes up a part of the lateral walls of the skull. It is a bilaterally symmetrical bone which is comprised of the squamous part, the tympanic part, styloid process, and the petrous part.

Just a few reminders here every time you think about the temporal bone: you remember that this bone is comprised by this different areas or structures.

And we can clearly see here the first one, highlighted in green. This is known as the squamous part of the temporal bone. And the squamous part of this bone makes up the lateral wall of the middle cranial fossa and also houses the middle meningeal artery.

Another bone that we can see here, now highlighted in green, this is known as the occipital bone.

The occipital bone is an unpaired bone that makes up a large portion of the basilar part of the neurocranium and houses, then, the cerebellum.

You can now see here a section of a large foramen at the base of the skull known as foramen magnum and through which the brain stem, the spinal branch of the accessory nerve, and the posterior and anterior arteries pass through. So this is an important foramen that you find on the occipital bone, and you can see here on this section of the skull.

Also other structures that will pass through this foramen include the vertebral artery and the spinal vein.

Also important to highlight here: a part of the occipital bone, which is known as the basilar part of the occipital bone. And the basilar part of this bone is located just anterior to the foramen magnum and sits adjacent to the petrous part of the temporal bone.

And you can see here the petrous part of the temporal bone, how it sits right next to the basilar part of the occipital bone.

Now, the pharyngeal tubercle is found on the inferior surface of the basilar part of the occipital bone. This is where both the pharyngeal constrictor muscle and the pharyngeal raphe insert.

Other part of the occipital bone that you can see here on the midsagittal section, this protrusion known as the external occipital protuberance.

On the other side of the squamous part of the occipital bone, there is a palpable prominence called, then, the external occipital protuberance and is located on the midline.

Though clearly visible and palpable on the external surface in this sagittal section, it appears merely as a small elevation.

Now, the external occipital protuberance serves as an attachment for, then, the trapezius muscle.

Still on the occipital bone, there is another structure worth highlighting here on the midsagittal section. This is known as the occipital condyle or occipital condyles even though we’re just looking at one. This is the midsagittal section. You would find another one on the remaining section, the other half of the skull.

Now, the occipital condyles are located just lateral to the foramen magnum, as you can see here. And there are kidney-shaped prominences that articulate with the first cervical vertebra forming, then, an important structure known or an important joint known as the atlanto-occipital joint.

The other structure that we see here on the midsagittal section, this is known as the sella turcica. And the sella turcica is formed by the body of the sphenoid bone. And this depression houses the pituitary gland.

We’re going to look at the different sutures that we find here on the midsagittal section. You see here part of the coronal suture, highlighted in green. And on this sagittal section, we take a look at this suture from the internal aspect as you can see here. And as we can also notice that it separates the frontal bone, notice here, from this bone here, which if you remember correctly, this is the parietal bone.

Another suture that I'm highlighting right now, this is known as the lambdoid suture, which separates this bone here, the occipital bone, from then the parietal bone… or parietal bones because it’s happening on both sides.

Like all the cranial sutures, the lambdoid suture is a fibrous joint.

In terms of the different foramina, we’re going to see this one here, highlighted in green. If you notice right about here, this is known as the jugular foramen which is formed by the petrous part of the temporal bone and the occipital bone.

Structures passing through the jugular foramen include, then, the glossopharyngeal nerve, the vagus nerve, the spinal accessory nerve, the inferior petrosal sinus, and also the sigmoid sinus, and also the posterior meningeal arteries. So a lot of important structures passing alongside or passing through the jugular foramen.

Another structure, another passage that you see here, highlighted in green, and we talked about before when we talked about the lesser wing, and the greater wing, and the sphenoid bone in general, this is the optic canal. And the optic canal is… encircles the optic nerve and also the ophthalmic artery, which will pass through this canal, and is found, then, on the sphenoid bone, as you can clearly see here on this image.

Another canal worth mentioning here that you see now, highlighted in green, this is known as the hypoglossal canal. And as the name indicates, the hypoglossal canal is located in the occipital bone. This is where the hypoglossal nerve will pass through.

We are ready now to move on to the next structure that you see here. This is also a little passage known as the external opening of the vestibular aqueduct.

The external opening of the vestibular aqueduct is located on the petrous part of the temporal bone at the posterior surface. And this structure is a small duct or canal that extends from the inner ear to the brain, and here, we find the endolymphatic duct.

The next one that you see here, highlighted in green, I already talked about, so we have here the foramen magnum, which is located on the base of the skull in the occipital bone. It is, as the name indicates, the largest foramen in the entire cranium and has, then, several structures passing through it, which include, then, the medulla oblongata, the vertebral arteries, and the spinal roots of the spinal accessory nerves.

The next one that you see, now highlighted in green, is known as the internal acoustic meatus. And the internal acoustic meatus is located at the posterior surface of the petrous part of the temporal bone.

And here, there are few structures that will pass through, which include, then, the facial nerve, the vestibulocochlear nerve, and the labyrinthine artery.

The next structures that you see now, highlighted in green, we already mentioned before, these are known as the arterial grooves. They are located on the inner surface of the parietal bones mainly, and they are caused by or they are formed by the arterial pressure from the middle meningeal artery, which causes the bone to, then, recede, as you can see here.

The next structure that you see here, highlighted in green, this is a groove for a sinus, more specifically the inferior petrosal sinus. And the groove for the inferior petrosal sinus is formed by the basilar part of the occipital bone and the petrous part of the temporal bone. This roof contains the inferior petrosal sinus which, along with other sinuses, will allow blood to drain from the center of the head.

Another groove that you see here, now highlighted, this is known as the groove for the superior petrosal sinus. And the groove for the superior petrosal sinus is located on the inner surface of the petrous part of the temporal bone, and it’s important to highlight here that it houses the superior, then, petrosal sinus.

Another groove that we see here, known as, then, the groove for the sigmoid sinus, and the groove for the sigmoid sinus is located on the inner surface of the temporal bone near the mastoid angle. And this is where the sigmoid sinus lies within this groove.

The next groove that you now see, highlighted in green, this is known as the groove for the transverse sinus and is located on the inner surface of the occipital bone, between the cerebral fossa and the cerebellar fossa.

Now, the transverse sinus runs along this groove.

Let’s talk about this sinus that you see here, highlighted in green, anteriorly. This is known as the frontal sinus. There are two frontal sinuses that are found on the squamous part of the frontal bone. They are located superior to the orbit and are separated by a septum.

The frontal sinus is one of the perinasal sinuses.

The next one that you see here, another sinus known as the sphenoidal sinus, the two sphenoidal sinuses, which are also perinasal sinuses, are made up by the body of the sphenoid bone. They are located behind the nasal cavity and are divided also by a septum.

Now, a few other structures worth remembering here on this tutorial, this is the anterior nasal spine, highlighted in green. The anterior nasal spine is a small, bony projection found anteriorly on the maxilla.

And the last structure of this tutorial will be this one that you see, highlighted in green, which is known as the anterior clinoid process, and it is formed by the lesser wing of the sphenoid bone.

This process provides then attachment for the tentorium cerebella… or the tentorium of the cerebellum.